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View Full Version : Lit GL_QUAD_STRIP??

12-13-2001, 04:53 PM
I have made up a simple Cube with using GL_TRIANGLE_STRIP and set one light.
The first Quad(first 4 vertices) are lit correctly, but the next quads(defined by 2 vertices each) are not. Only the right side is lit, cause the new normal vector is only applied to the 2 new vertices. How can i fix this problem?

Here is a short piece of code:

glNormal3fv(normalize_vec(torso[0], torso[1], torso[2]).vec_array);
glVertex3fv(torso[0].vec_array);
glVertex3fv(torso[1].vec_array);
glVertex3fv(torso[3].vec_array);
glVertex3fv(torso[2].vec_array);
glNormal3fv(normalize_vec(torso[3], torso[4], torso[5]).vec_array);
glVertex3fv(torso[5].vec_array);
glVertex3fv(torso[4].vec_array);
glNormal3fv(normalize_vec(torso[5], torso[6], torso[7]).vec_array);
glVertex3fv(torso[7].vec_array);
glVertex3fv(torso[6].vec_array);
glNormal3fv(normalize_vec(torso[7], torso[8], torso[9]).vec_array);
glVertex3fv(torso[9].vec_array);
glVertex3fv(torso[8].vec_array);
glEnd();

mikael_aronsson
12-14-2001, 03:01 AM
Hi !

The order of the vertices is odd for quad strips. after the first two vertices it goes like this:

2n-1, 2n, 2n+2, and 2n+1, notice the order 2n+2 and 2n+1 the last two are reversed.

I think this is your problem, you have to reorder the vertices a bit.

Mikael

12-14-2001, 03:44 AM
To order of the vertices I usesd is correct I think( or better hope!? http://www.opengl.org/discussion_boards/ubb/wink.gif ).
I have found a few other examples in the net, but there's the problem, i put the important lines of code into my files and there's the same problem, the first quad is lit correctly, the others not -> only the right side of the quads are lit(if I move the light straigt along the axis).
Here is more code(forgot it to post, last time):

nv_scalar lightPos[] = { 0.0f, 6.0f, 0.0f, 1.0f};
nv_scalar spotDir[] = { 0.0f, -1.0f, 0.0f};
nv_scalar ambientLight[] = { 0.3f, 0.3f, 0.3f, 1.0f};
nv_scalar diffuseLight[] = { 0.7f, 0.7f, 0.7f, 1.0f};
nv_scalar specularLight[] = { 1.0f, 1.0f, 1.0f, 1.0f};

vec3 torso[] = { vec3(-1.5f, -1.5f, 1.5f),
vec3(-1.5f, 1.5f, 1.5f),
vec3( 1.5f, 1.5f, 1.5f),
vec3( 1.5f, -1.5f, 1.5f),
vec3( 1.5, 1.5f, -1.5f),
vec3( 1.5, -1.5f, -1.5f),
vec3(-1.5f, 1.5f, -1.5f),
vec3(-1.5f, -1.5f, -1.5f),
vec3(-1.5f, 1.5f, 1.5f),
vec3(-1.5f, -1.5f, 1.5f) };

glFrontFace(GL_CW);
glLightfv(GL_LIGHT0, GL_POSITION, lightPos);
glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, spotDir);
glLightfv(GL_LIGHT0, GL_AMBIENT, ambientLight);
glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuseLight);
glLightfv(GL_LIGHT0, GL_SPECULAR, specularLight);